The engine of a conventional supersonic aircraft includes a center body having an elongated compression surface to help improve pressure recovery caused by movement of the engine through the air at supersonic speeds. The compression surface, together with other features of the aircraft's propulsion system, slows the supersonic airflow entering the propulsion system to a speed that is compatible with the turbo machinery of the engine.
One undesirable consequence of having an elongated compression surface is the buildup of a relatively thick boundary layer on internal surfaces of the inlet (e.g., portions of the diffuser). The boundary layer is a portion of the airflow located proximate a viscous surface (such as the compression surface and the surface of the diffuser) that, because of its interaction with the viscous body, moves slower than the free stream velocity.
Because the boundary layer air is moving at a slower speed than the remainder of the airflow, the boundary layer air will have a lower stagnation pressure than the remainder of the airflow. This leads to distortion in the stagnation pressure of the airflow entering the Aerodynamic Interaction Plane (“AIP”) (e.g., the fan or the face of the engine). This distortion in stagnation pressure is undesirable, because it may adversely impact both engine operability and performance.
Several different solutions have been developed to combat the distortion in the stagnation pressure caused by the elongated compression surface. For example, some propulsion systems bleed the boundary layer from the airflow by passing the airflow over a porous surface and using low pressure to extract the boundary layer from the airflow. While this is effective at diminishing the thickness of the boundary layer, such bleed systems add cost, complexity, and weight to a propulsion system.
Another solution has been to position vortex generators of modest height on the center body. These vortex generators have a height ranging from twenty percent to forty percent of the local boundary layer thickness and generate vortices that propagate completely within the boundary layer. These vortices increase the energy level of the boundary layer which, in turn, allows the boundary layer to remain more robustly attached to the curving surface of the center body or other inlet surface. While this inhibits growth and separation of the boundary layer, it does not modify its structure or appreciably reduce its thickness and the stagnation pressure of the air entering the AIP remains distorted.
Accordingly, it is desirable to provide a propulsion system that reduces distortion of the stagnation pressure of the airflow entering the AIP. Additionally, it is desirable to provide a supersonic aircraft equipped with a propulsion system that reduces the distortion of the stagnation pressure. Furthermore, other desirable features and characteristics will become apparent from the subsequent summary and detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.